Technical–economic assessment of stone slabs surface finishing using water jet technology

Abstract

This paper examines, from an economic standpoint, some of the surface finishing results achieved for stone slabs using high pressure water jets. The results of both the management accounting method and a technical and economic cost analysis method are here applied. The latter method is specifically aimed at verifying and fine-tuning the management analysis model based on the technical coefficient matrix. The second method proposed allows one to examine each process in detail and easily determine technical–economic models for planning, processing and management. The type of production cost analysis proposed here is original, rigorous and precise. The fact that it captures all the most significant technical aspects of the process and clarifies their economic implications makes it far more preferable to the traditional final accounts analyses. Moreover, this technical and economic cost analysis method allows one to accurately calculate the unit cost of each product.

Appendix. Nomenclature

a _ik :

technical coefficient of the factor or production F _ik in the kth process for the Q _k production level

AF:

area exposed to water jet during process

APF:

total area of finished product

c _a :

hourly cost of abrasive

c _cw :

hourly cost of cooling water

c _d :

hourly depreciation costs

c _fw :

hourly cost of finishing water

c _ins :

hourly insurance costs

c _int :

hourly interest costs

C _l :

cost of 1 worker (annual)

c _l :

hourly labour cost

c _m :

hourly cost for maintenance and replacement of spare parts and other mechanical components

Cm _k  = c _k :

average production cost

c _n :

hourly cost of nozzle

C _n :

unit cost of nozzle

c _o :

total hourly cost

c _op :

total hourly operating costs

c _ow :

total hourly ownership cost

c _p :

hourly cost of power

C _p :

cost per unit of electricity

CSMF:

cost per square meter of finishing

c _t :

hourly cost of focusing tube

C _t :

unit cost of focusing tube

c _tax :

hourly property tax rate

C _w :

cost per unit of water

d _n :

nozzle diameter

DP:

delivered price

EE:

electrical power consumed

EE _k :

cost efficiency of the production process Q _k

EOP:

estimated ownership period

ET _ik  = Qm _ik :

average productivity of the factor F _i for that level Q _k of production

EU:

estimated usage

F _i :

ith factor of production

i :

distance between passes

MdT:

matrix of technical coefficients

MP _i :

market price of the ith stone

N _d/y :

working days per year

N _h/d :

number of hours per shift

NP:

number of marketable slabs

OU:

ownership usage

P :

water pressure

p _h :

hydraulic power

P _k :

selling price of kth product

PL:

path length

p_ma :

energy for movement and auxiliary equipment

p_P :

energy absorbed by pump

p _t :

time required to move and prepare slab S _i

Q _a :

mass flow rate of abrasive

Q _cw :

cooling water flow rate

Q _k :

kth production process

Q _wj :

water-jet flowrate

R _ins :

insurance rate

R _int :

interest rate

R _tax :

property tax rate

RVR:

residual value at replacement

sc_C :

stream-contraction coefficient

S _i :

ith slab

sl _f :

focus tube service life

sl _n :

nozzle service life

SV:

volume of S_i

s _wj :

jet velocity

t _i :

slab thickness

Ul _k :

average gross profit

Ulp:

total gross profit

V _i :

unit price of factor F _i

VPF:

total volume of finished product

v _t :

travel speed

v _w :

surface finishing velocity

WL:

work length

γ _m :

operator/machine productivity coefficient

δ _m :

use of human resources during water jet finishing process

ρ _P :

pump efficiency