The primary roof support systems used in coal mines include headed rebar bolts typically 4 feet to 6 feet in length, ¾ inch and ⅝ inch in diameter, and used in conjunction with resin grouting in 1 inch diameter holes.
Multi-compartment resin cartridges are used to supply the resin grouting for the support systems. Among the cartridges known for this purpose are those disclosed in U.S. Pat. No. 3,795,081 to Brown, Jr. et al., U.S. Pat. No. 3,861,522 to Llewellyn et al., U.S. Pat. No. 4,239,105 to Gilbert, and U.S. Pat. No. 7,681,377 B2 to Simmons et al., the entire contents of each being incorporated herein by reference thereto. Cartridges typically are available in a variety of lengths ranging from 2 feet to 6 feet and in diameter from ¾ inch to 1¼ inch. The cartridges also typically include two compartments: a first compartment with a reinforced, thixotropic, polyester resin mastic (a fluid) therein, and a second compartment with an organic peroxide catalyst (also a fluid) therein. The resin and catalyst are segregated from one another in order to prevent a reaction prior to puncturing of the compartments to allow contact and mixing to occur.
In use, a cartridge and bolt (or other reinforcing member) are placed in a borehole so that they abut one another. In order to puncture the cartridge so that the contents of the compartments may be released and mixed, the bolt for example may be rotated in place to shred the cartridge, thereby mixing the components and permitting solidification of the mastic. Mixing of the resin and catalyst (due to cartridge rupture as well as spinning of the bolt in the borehole) results in hardening that allows the bolt to be held in place.
There has long been a need, heretofore unsolved and unmet, for a resin cartridge that remains generally firm prior to use in a borehole in a mine for retaining a bolt in place. Known resin cartridges, as described above, have limited firmness due to the pressure of the resin/and or catalyst in the compartments of the cartridge. In other words, because the compartments are substantially filled and sealed at the time of manufacture, the cartridges tend to have some limited resistance to bending. However, over time, the cartridges have a tendency to become limp. The rapid loss of firmness that occurs after cartridge manufacture is due to several factors including creep of the packaging film as well as loss of some of the contents from the cartridge due to diffusion through the film that forms the cartridge or leakage proximate the ends of the cartridge. The catalyst used in the multi-compartment cartridges, for example, is water-based, and water diffuses from the catalyst through the cartridge film. Polyester film typically is used to form the cartridge; polyester is substantially impermeable with respect to the resin, but not water in the catalyst. The polyester film typically is between 0.001 and 0.005 inch thick. Although multi-layered films could be used or films with metal coatings to decrease the loss of water through the film, this adds expense and would not solve all of the rigidity issue.
Cartridges typically are manufactured and sold in bulk and often are not used immediately after manufacture. The loss of rigidity from the as-manufactured state can occur for example over a period of 1 week to 6 months prior to use of the cartridge in a mine, and cartridge limpness is one of the primary reasons that cartridges are discarded prior to use or rejected by customers purchasing the cartridges. This is because limpness causes the cartridge to buckle at one or more locations over its length when handled by mining personnel. When the cartridges is installed in a borehole in the roof of a mine, for example, it is held from a bottom end and inserted in the hole. However, due to the long length of the cartridge coupled with the loss of rigidity, the cartridge can be difficult to insert in the hole because it flops over when oriented vertically. This can be analogized to pushing a wet noodle into a hole of similar size, i.e., a difficult task. Thus, there is a need for a cartridge that does not have such a “shelf-life” issue, e.g., that remains generally stiff prior to installation in a borehole.
When multi-compartment resin cartridges are manufactured, such as in the form of partitioned film packages, a series of cartridges may be formed using a package-forming apparatus. The cartridges may be separated from one another at a clipping head associated with the package-forming apparatus, where the cartridges are cut from one another and sealed. Alternatively, a series of cartridges may be separated from one another in a different operation from the cartridge forming operation, i.e., off-line using a cutter separate from the clipping head. In particular, the cartridges may be separated from one another proximate their clipped ends, i.e., proximate the regions of the opposite ends of the cartridges which are each clipped so as to retain the resin and catalyst in the package. Thus, before being separated, adjacent cartridges have two clips adjacent each other with some cartridge packaging disposed therebetween. A cut is made between the adjacent clips to separate the cartridges.
U.S. Pat. No. 4,616,050 to Simmons et al. discloses filler-containing hardenable resin products. In particular, a hardenable resin composition is disclosed that is adapted for use in making set products, e.g., a hardened grout for anchoring a reinforcing member in a hole. A course/fine particulate inert solid filler component, e.g., limestone and/or sand, is used. In one composition, a resin component and a catalyst component are provided in a 70:30 percentage ratio. In one example, the resin component is describes as a mixture of 21% of a resin formulation and 79% filler (limestone or limestone in combination with sand). The base resin formulation consisted approximately of 64.0% of a polyester resin, 17.1% styrene, 14.2% vinyl toluene, 1.9% fumed silica, and 2.9% stabilizers and promoters. The polyester resin was the esterification product of maleic anhydride, propylene glycol, and diethylene glycol, the maleic anhydride having been partially replaced with phthalic anhydride (30% maleic anhydride, 23% phthalic anhydride, 17% propylene glycol, and 30% diethylene glycol). The catalyst component was a mixture of 72.5% filler (i.e., limestone), 19.1% water, 0.4% of methylcellulose, and 8.0% of a benzoyl peroxide (BPO) catalyst paste consisting, approximately, of 49.3% BPO, 24.7% butyl phenyl phthalate, 14.8% water, 7.9% polyalkylene glycol ether, 2.0% zinc stearate, and 1.3% fumed silica. Two grades of limestone were used as specified in Table I, and both “coarse” and “fine” filler particles were used. Examples of disclosed compositions are as follows:
TABLE IProductFillerProduct IFiller in Resin: [12.5% coarse particles and 87.5% fine particles]38% “Grade A” limestone: 33% of the particles averaged largerthan 1.19 mm (with 10% of these larger than 2.3 mm,3% larger than 4.76 mm, and none larger than 9.53 mm);an average of 42% of the particles were smaller than 0.59 mm(with 17% smaller than 0.297 mm, and 5% smaller than0.149 mm)62% “Grade B” limestone: an average of 99.8% of theparticles were smaller than 0.84 mm, with 98.7% smallerthan 0.297 mm, 97.9% smaller than 0.250 mm,91.5% smaller than 0.149 mm, and 69.6% smaller than 0.074 mmFiller in Catalyst: 100% Grade B limestoneProduct II Filler in Resin: [31.9% coarse particles and 68.1% fine particles]38% sand: 83.9% of the particles averaged larger than1.00 mm (with 59.6% of these larger than 1.19 mm);6.6% of the particles averaged smaller than 0.84 mm(with 1.9% smaller than 0.59 mm, 0.8% smaller than 0.42 mm,and 0.2 smaller than 0.297 mm)62% Grade B limestoneFiller in Catalyst: 100% Grade B limestoneProduct IIIFiller in Resin: 100% Grade B limestoneFiller in Catalyst: 100% Grade B limestoneProduct VFiller in Resin: [12.4% coarse particles, 87.6% fine particles]37.5% Grade A limestone62.5% Grade B limestoneFiller in Catalyst: 100% Grade B limestoneProduct VIFiller in Resin: 62.5% Grade B limestone37.5% coarse sand all particles passed through a 3.18-mmscreen and were held on a 1.59-mm screenFiller in Catalyst: 100% Grade B limestone
As used herein, the terms “grouting,” “grouting system,” “grout,” and “grout system” mean a substance that hardens to anchor a reinforcing member in a space. For example, grouting can be provided in the form of a cartridge with a compartment housing a polyester resin and a compartment housing an initiator/catalyst, such that when the cartridge is shredded and the resin is mixed with the initiator/catalyst, a reinforcing member can be anchored in a space.
In manufacturing grouting, from a materials cost perspective, as more filler is used the cost becomes less expensive. In other words, the more filler used instead of actual resin or catalyst, the less expensive the materials required to form the composition. Moreover, filler permits better performance to be achieved by increasing the strength of the hardened grout. However, the tradeoff with using more filler in a composition is that the composition becomes more viscous. For example, the more that filler is used in the resin, the more difficult it is to pump the resin mastic into the package (cartridge) because the resin becomes “thick” (the viscosity increases). High resin mastic pumping pressures become necessary with such high viscosity compositions. Also, the more that filler is used in the overall grouting composition, the more difficult it becomes for the mine bolt to be able to penetrate the cartridge when spun.
In basic principle, when larger (e.g., coarse) filler particles are used in a composition, the particles overall provide lower surface area than when smaller (e.g., fine) particles are used. Use of such larger particles thus permits a lower viscosity grouting and advantageously aids in shredding of the cartridge and mixing of the cartridge components. In contrast, smaller (e.g., fine) particles can have a very substantial effect on viscosity of a composition because of the high overall surface area that they provide. The use of larger (e.g., coarse) filler particles involves other tradeoffs as well. The resin and catalyst are delivered to the packaging (cartridge) through so-called fill tubes, which are sized to be accommodated with respect to the compartments of the cartridge. The fill tubes thus can only be of a certain diameter in order to be used in the cartridge manufacturing process. The internal diameter of the fill tubes limits the size of the filler particles that can be delivered through those tubes. Separately, when cartridges are clipped at either end during the manufacturing process to seal the resin and catalyst within the cartridge, larger diameter particles can interfere with the clips, causing leakage of resin or catalyst proximate the cartridge free ends and/or rupture of the cartridge when the cartridge is squeezed during installation of a clip. For example, large solid particles can lodge under the metal clips and rupture the cartridge film due to their sharp edges or form passages that allow the resin to slowly leak from the cartridge ends. Leakage of resin can be problematic because the cartridges can become messy to handle and also can become stuck to one another.
The use of larger diameter filler particles thus can result in a higher rejection rate of manufactured product due to quality control. For these reasons, it is known that clipping requirements are a limiting factor in the filler particle size used in grouting. Prior art compositions, for example, have had a maximum particle size of 3/16 inch. But even then, if a particle of such maximum size is present proximate a clip, the cartridge typically ruptures and has to be discarded rather than sold. It is for this reason that during cartridge manufacture, only a small percentage of larger (e.g., coarse) filler particles are used (e.g., 0-5%) such that the number of rejected cartridges due to leakage and/or rupture remains tolerable (e.g., 1-2%).
Regardless of the size of the filler particles, the presence of any resin on the clipped ends can be problematic because the resin contains volatile styrene that can be smelled in concentrations as low as 1 part pre million. Thus, warehouses, trucks, and storage areas used for the cartridges become unpleasant due to the strong smell of styrene. The escape of styrene to the atmosphere also is an environmental hazard. There is a need for cartridge clipping in which the areas proximate the clips remain substantially free of resin/styrene (such that all the styrene is used during the reaction when the resin mastic is mixed with the catalyst mastic). Form fill hardware already in use for forming the cartridges use rollers to squeeze the outside of the cartridge in the areas to receive a clip, just before the clip is applied. While such an approach works for cartridges with resin mastic and/or catalyst mastic that do not have high filler levels, compositions with high filler levels prevent the rollers from adequately expelling mastic from proximate the ends of the cartridge and in any case leave a film of resin on the surface of the cartridge with styrene that evaporates into the atmosphere.
Given that the use of fillers was contemplated in resins for mine bolt grouting since at least the mid-1960s, e.g., as disclosed in U.S. Pat. No. 3,731,791 to Fourcade et al., there has been a long-felt but unsolved need for methods and apparatuses for addressing cartridge clip leakage elimination. There also has been a long felt but unsolved need for methods and apparatuses for stiffened cartridges.
Another type of cartridge used today is a dry cement packaged in a porous membrane cartridges (Tyvek, Canvas, etc.). The cartridges are typically 25 to 32 mm in diameter and 0.5 to 2 meters in length. In use, the cartridge is submerged in a container of water for 1 to 5 minutes; water permeates the membrane and diffuses into the cement. The cartridge then is inserted into the borehole and the mine bolt is inserted to puncture the cartridge. The cement typically hardens in 10 minutes to 24 hours. Among the disadvantages to this type of cartridge are that it is very labor intensive to package the dry cement in long, small diameter cartridges, it is very labor intensive in the mine to submerge the cartridges in water, there is great sensitivity to the time the cartridge is submerged in water (too short and not enough water, or too long and too much water), and the setting time must be long so the cement does not set when cartridge is soaking in water. Thus, there is a need for an improved cartridge.