1. PLANTEAMIENTO DEL PROBLEMA
1.4 OBJETIVOS DE LA INVESTIGACIÓN
1.4.2 Objetivos específicos
All crushers require some type of backing when replacing the crushing wear members. Epoxy resin backing com- pounds have all but eliminated the possibility of workers being accidentally burned due to molten zinc either spilling or exploding when it comes in contact with wet surfaces. Epoxy backing will flow into spaces where zinc will not, thus providing more solid support.
Epoxy backing is designed for impact resistance, com- pressive strength, chemical resistance and economy of installation. In its cured form, epoxy backing also resists most solvents, greases, oils, acids and alkalies that are found around construction machinery. Long term expo- sure to water may ultimately weaken regular backing.
Applications
As a backing for crusher wearing parts, epoxy backing has a relatively high impact strength when tested on a “Bond Impact Tester.” The recommended backing for SUPERI- OR gyratory crushers is a high performance epoxy back- ing with a compressive strength of 18,000psi (124 Mpa). The backing should also have good water resistance and low shrinkage properties. The 22-pound (10 Kg) kit pro- vides 358 cubic inches (5866 cm3) of backing.
NOTICE
In order to obtain these fully cured properties, the whole process of mixing, pouring, and maintaining the correct temperatures of the epoxy backing and the adjacent ma- chinery parts must be strictly controlled.
Precautions when Using Epoxy Backing
WARNING
Carefully follow the instructions as well as the precau- tions that are printed on the individual containers of epoxy before mixing and pouring. Skin contact with
THE USER NEEDS TO STRICTLY CONTROL THE COMPLETE PROCESS OF STORAGE, MIXING, POUR- ING, AND MAINTAINING CORRECT TEMPERATURES OF THE EPOXY BACKING AND MACHINERY PARTS AS CALLED FOR IN THESE DIRECTIONS. METSO MINER- ALS MAKES NO WARRANTY WHETHER EXPRESSED OR IMPLIED INCLUDING THE IMPLIED WARRANTY OF MERCHANTABILITY AND USER ASSUMES ALL RISK WITH RESPECT TO THE FITNESS OF THIS PRODUCT FOR HIS USE.
Storing Epoxy Backing
Unopened and undamaged kits of epoxy backing have a limited shelf life of one year. Do not store where tempera- tures exceed 90° F (32.2° C) or below 32° F (0° C) for lon- ger than 6 months. Rotate any stock on hand to avoid ex- ceeding storage limits. The batch number stamped on the label on each container shows the date when packaged. Do not attempt to mix partial containers of epoxy backing. Do not add foreign material to the backing.
Temperature Affects Cure
When curing, the hardener and resin portions react and generate heat. Epoxies are good insulators and, in large masses, the internal heat build-up will shorten the working time.
When poured in thin sections, along with natural heat loss to surrounding materials, cure takes longer.
The optimum temperature range for mixing and pour- ing epoxy backing is 70--80° F (21--26.6° C). When air tem- perature is below 60° F (15.6° C), warm unmixed ingredi- ents to the 70--80° F (21--26.6° C) range. If air temperature is above 90° F (32.2° C), cool ingredients by immersion in cool water or store in air conditioned room, to optimum temperature range of 70° F -- 80° F (avoid getting water into the contents of containers).
NOTICE
The time required for a complete cure for epoxy backing used for backing crusher wear parts depends on envi- ronmental temperature. Full compressive strength may
SUPERIOR MK- II
Gyratory Crushers
Section 4 —
Installation
M--010704--TAW--01 50 (10) 60 (16) 70 (21) 80 (27) 90 (32) 0 5 10 15 20 25 30TEMPERATURE OF CONCAVES OR MANTLES, _F (_C)
CURE
TI
ME,
H
OURS
FIG. 4-30 — Epoxy Backing Cure Time Versus Temperature
NOTICE
Pouring into or against cold machinery will adversely af- fect curing. Parts to be filled must be warmed to 70 -- 80° F (21 -- 26.6° C).
Effect of Moisture
Epoxy backing can be poured into damp areas, although it will not adhere to damp surfaces. Small amounts (sever- al grams) of water accidentally entrained into the material during mixing will alter the cure time and cause the back- ing to be slightly porous. If greater amounts of water be- come entrained in the material during mixing, it will lose its strength characteristics and become unusable.
Preparation of Machine Parts Backing Crusher Parts
1. Prepare all parts by removing all oil, grease, scale, rust, dirt, etc. from surfaces to be bonded. Epoxy backing is normally bonded to wearing parts only and this especially applies to self tightening crusher man- tles.
2. Where necessary, coat surfaces not to be bonded with silicone spray or another release agent to prevent bonding. DO NOT USE GREASE OR HEAVY OILS FOR THIS PURPOSE.
3. Assemble the mating parts.
4. Seal all holes and open joints with plaster of Paris to prevent leakage of epoxy backing.
5. Protect threaded parts with clay or putty dams to direct flow away from threads.
6. To provide for proper flowing and curing of epoxy backing at temperatures lower than 60° F (15.5° C), warm parts to be bonded, and unmixed epoxy back- ing, to 70 - 80° F (21 - 26.6° C).
CAUTION
Adequately vent working area when heating crusher parts and do not create fire hazards.
SUPERIOR MK- II
Gyratory Crushers
Section 4 —
Installation
Mixing Epoxy Backing
Epoxy backing resin must be mixed thoroughly and uni- formly with hardener before using. Otherwise it will not flow and cure properly.
When mixing an entire kit, 22 pounds (10Kg) of resin, with hardener supplied, follow these instructions:
1. When air temperature is lower than 60° F (15.6° C), warm unmixed epoxy backing to 70 - 80° F (21-26.6° C). 2. When air temperature is above 90° F (32.2° C) cool unmixed epoxy backing to 70° - 80° F (21° - 26.6° C) by immersion of closed and sealed container in cool water.
3. Pre-mix resin thoroughly with power drill and stirring rod, scraping bottom and sides of container. Mix for one to two minutes. Do not exceed 850 rpms. 4. Add entire contents of hardener container and contin-
ue power mixing until mixture is completely uniform in color (streaks of color in mixture or around edge indi- cate further mixing is required).
5. Use of less than full kits of epoxy backing for crusher wear surface backing is not recommended.
CAUTION
Mix and pour epoxy backing only in quantities that allow complete usage before working life is exceeded.
Pouring Epoxy Backing
Pour mixed epoxy backing immediately. Hardening be- gins when hardener is added to resin. Mixed epoxy back- ing (at 70° F or 21° C) will harden into a solid mass in ap- proximately 20 minutes if left in the container. This
hardening time is extended to 30-40 minutes if pouring is started immediately after mixing. This extended harden- ing time occurs when epoxy backing is in thin sections or between cooler surfaces.
Backing Crusher Parts
1. For uniform distribution, pour mixture at several points around the cavity.
2. Additional batches of epoxy backing can be poured with positive bonding results.
NOTICE
When pouring epoxy backing behind gyratory crusher concaves, flow difficulties may be avoided if poured in quantities to fill no more than one tier of concaves at a time.
Quantity Requirements
For estimating quantity requirements, refer to the follow- ing table.
NOTICE
If concaves are supplied with the backs paneled out, fill the panels with grout, or more epoxy backing material will be required than was supplied with your crusher. Also note that thicker sections of epoxy backing allow more shrinkage. For thick sections, a second pour may be advisable.